Method for monitoring operations of an internal combustion engine to detect combustion misses

ABSTRACT

A method is proposed for monitoring operations of an internal combustion engine to detect combustion misses for internal combustion engines having dual spark coils. A method is provided for the primary-side monitoring of the spark voltage and/or of the spark duration, and a method is provided for detecting irregular operations. If a faulty ignition is detected in one cylinder at one spark plug by monitoring the spark voltage and/or the spark duration, the second spark plug in this cylinder is then cut off (de-energized) and the reaction to this cut-off is monitored by means of the method for detecting irregular running. If the irregular running detection confirms faulty operation of the internal combustion engine, then the faulty ignition at the first spark plug of a cylinder was correctly recognized and appropriate emergency measures are introduced.

FIELD OF THE INVENTION

The present invention is based on a method for monitoring operations ofan internal combustion engine to detect combustion misses.

BACKGROUND INFORMATION

A method is described in German Patent Publication No. 40 35 957, or inthe corresponding U.S. Pat. No. 5,201,293, in which a primary-sidemonitoring of the spark voltage and/or of the spark duration, as amethod for detecting ignition misfirings, is so combined with a methodfor measuring irregular running, as a recognition of combustion misses,that at least one of the two methods will work under every engineoperation condition, and that under those engine operation conditions,in which one of the two methods yields inaccurate results, the methodyielding inaccurate results is masked out (suppressed), the consequencebeing that only the other method is performed each time. In those cases,in which both methods are performed, the results of the various methodscan be examined in a plausibility check to reduce the risk of faultymonitoring results.

Individual methods for monitoring operations of the internal combustionengine are also described in European Patent Application No. 0 344 349,for example, which shows a primary-side monitoring of the sparkduration. A method for detecting irregular operation of the internalcombustion engine is described in U.S. Pat. No. 4,691,288.

SUMMARY OF THE INVENTION

In contrast, the method according to the present invention isadvantageous in that, when working with internal combustion engineshaving two spark plugs per cylinder, a recognition of ignition misfiringat the first spark plug in one cylinder is monitored by applying theirregular-running method after the second spark plug in this cylinderhas been de-energized.

Accordingly, it is possible to diagnose a twin-spark ignition byselectively de-energizing the spark plugs. Therefore, the presentinvention provides a reliable method for detecting combustion misses, inparticular at high speeds and loads.

Another embodiment of the present invention allows, for example, after amalfunction is detected at one spark plug, to shut off the injectioninto a specific cylinder in order to prevent unburned (combustible)mixture from getting in the exhaust.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of an internal combustion engine having dualspark coils for implementing the method according to the presentinvention.

FIG. 2 shows a sequence of process steps for monitoring operations ofthe internal combustion engine according to the present invention.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary design of an internal combustion engineincluding dual spark coils and the sensing (recording) of quantitiesrequired for monitoring operations of the internal combustion engineaccording to the present invention. An exemplary four-cylinder internalcombustion engine is illustrated in FIG. 1. It is possible to have otherinternal combustion engines with more cylinders, as well. In theinternal combustion engine as shown in FIG. 1, four ignition coils ZS1,ZS2, ZS3, ZS4 are provided, each consisting of a primary winding and ofa secondary winding. The primary winding of each ignition coil isconnected, for example, to the supply voltage U_(V), e.g. to the batteryof the internal combustion engine. The other side of the primary windingis connected respectively to ground via transistor output stages T1, T2,T3, T4 for driving the current flow in the primary windings of ignitioncoils ZS1, ZS2, ZS3, ZS4. Each end of the secondary winding of eachignition coil is connected to a spark plug. In this embodiment of thepresent invention, the spark plugs which are fed by an ignition coil,are installed in various cylinders so that these cylinders are offset(staggered) from one another by a 360° arc of crankshaft rotation in thecompression stroke. Thus, in the basic design according to the presentinvention as shown in FIG. 1, the spark plugs 1 and 2 of the cylinder Z1are fed, on the one hand, by the ignition coil ZS1 and, on the otherhand, by the ignition coil ZS3. Also, the spark plugs 3 and 4 of thecylinder Z2 are fed by the ignition coils ZS2 and ZS4. The output stagesT1 through T4, which switch on and off the current flow in the primarywindings of the ignition coils, are driven by a control unit 5.Accordingly, the signals of the sensors (not shown) for detecting theoperating parameters such as speed n, pressure p, temperature T, and thelike are conducted (transmitted) to the control unit 5. On the basis ofthe detected operating parameters, the control unit 5 determines thepoint of ignition and the dwell period for the individual ignitioncoils. A voltage tap is placed in each series connection which includesa primary winding and a transistor output stage, so that a signalcorresponding to the spark voltage transmitted to the primary side isconducted for each ignition coil to the control unit 5. The sparkvoltage transformed to the primary side is evaluated in the control unit5. According to the present invention, the spark duration can bedetected and compared to specified values. Another embodiment of thepresent invention allows a spark voltage characteristic to be comparedwith a stored spark voltage characteristic so that an error is generatedif there is a discrepancy. The control unit 5 continues to drive theinjectors E1, E2, E3, E4, so that the process of injecting theindividual cylinders is controllable by the control unit 5 for eachindividual cylinder.

FIG. 2 shows individual process steps for implementing the method inaccordance with the present invention. The individual process steps areillustrated in FIG. 2 on the basis of the exemplary design according tothe present invention as shown in FIG. 1.

Work step 20 provides for a detection of the quantities for implementingthe monitoring operations of the internal combustion engine in thecontrol unit 5. Thus, the spark voltage U_(PR) provided on the primaryside of the ignition coils is detected for a specific cylinder in whichan ignition has just occurred and has been compared with determinablevalues. At the same time, the speed of the internal combustion engine ismeasured by an rpm sensor. Thus, the primary voltage U_(PR1) whichrepresents the spark voltage characteristic at the spark plug 1, isdetected for ignition in cylinder Z1. As already explained, thisdetected primary voltage characteristic is evaluated in a subsequentquery 21. If a faulty spark voltage is determined, then the "N" outputof query 21 leads to work step 22, in which the ignition coil ZS3, whichsupplies the spark plug 2 (connected in parallel to the spark plug 1)with high voltage in cylinder Z1, is switched off. In work step 22, suchswitch-off operation performed by the ignition coil ZS3. By switchingoff a high secondary voltage supplied to the spark plug 2, subsequentcheck is performed in query 23 whether an irregular operation of theinternal combustion engine is determined after a completed ignition inthe cylinder Z1. If an irregular operation was determined in the query23, then the ignition in the cylinder ZS1 is recognized as faulty inwork step 24, which is connected to the "Y" output of query 23.Emergency measures are then triggered in work step 25, such as switchingoff the injection in cylinder Z₁. If the query 23 was answered in thenegative (i.e., directed to "N" output of query 23), it is thenestablished in work step 26 that the ignition in cylinder Z1 wasacceptable, which, in turn, means that the spark plug 1 has produced asuitable spark. Thus, the faulty spark voltage at the spark plug 1originally determined in query 21 has not been confirmed by theirregular running method, and the supplying of the ignition coil ZS3 canbe switched on again in work step 27. The process subsequently startsagain in work step 28 by returning to the beginning of the process.

What is claimed is:
 1. A method for monitoring operation of an internalcombustion engine to detect combustion misses, the internal combustionengine including at least one ignition coil, at least one cylinder andat least two spark plugs, first and second of the at least two sparkplugs being associated with one of the at least one cylinder, the methodcomprising the steps of:monitoring at least one of a spark voltage and aspark duration to detect an ignition misfire in the internal combustionengine; supplying a high secondary voltage using the at least oneignition coil; switching off a first ignition coil of the at least oneignition coil when the ignition misfire is detected at the first sparkplug of the one of the at least one cylinder during an ignition cycle,the at least one ignition coil supplying the high secondary voltage tothe second spark plug of the one of the at least one cylinder;activating an irregular operation monitoring of the internal combustionengine; and detecting the ignition misfire of the first spark plug whenirregular operation of the internal combustion engine is detected. 2.The method according to claim 1, further comprising the step ofrecognizing a correct operation of the first spark plug when theirregular operation of the internal combustion engine is not detected.3. The method according to claim 1, further comprising the step ofswitching off an ignition to the one of the at least one cylinder whenthe ignition misfire of the first spark plug is detected, the ignitionbeing switched off by shutting off a fuel injection to the one of the atleast one cylinder and by de-energizing the at least one ignition coil.